Control for an I.S. machine

ABSTRACT

A control for a glass forming machine is disclosed which receives as an input the event angles used to control the machines operation. These event angles, which define the time in a cycle when each event is turned on and off, are unwrapped to represent times in the glass forming process which takes more than two machine cycles to complete. A computerized model of the unwrapped cycle is defined and a control analyzes the computerized model as a constrained optimization problem to define an optimized schedule of event times and defines a plurality of intermediate event time schedules in an incremental application.

The present invention is a continuation-in-part of U.S. patentapplication Ser. No. 10/980,502, filed Nov. 3, 2004, now abandoned.

The present invention relates to an I.S. (individual section) machineand more specifically to a control for such a machine.

BACKGROUND OF THE INVENTION

An I. S. machine includes a plurality (usually 6, 8, 10, or 12) ofsections. Each section has a blank station including a mold opening andclosing mechanism having opposed mold supports which carry blank moldhalves. The mold supports are displaced by a suitable motor such as apneumatic cylinder or profiled actuator (servo motor) between open andclosed positions. A gob of molten glass will be delivered to the closedblank mold. The open top of the blank mold will then be closed by abaffle, which is displaced from a remote position to an advancedposition by a suitable motor. The gob will be formed into a parison inthe blank mold and after the surface of the parison is sufficientlycooled, the baffle will be retracted, the mold supports will beretracted and a pair of neck ring holder arms, which are rotativelysupported by an invert mechanism, will be rotated 180 degrees todisplace the parison to a blow station. The blow station also includes amold opening and closing mechanism having opposed mold supports carryingblow mold halves. These mold supports are displaced between open andclosed positions by a suitable motor. With the parison located at theblow station, the mold supports are closed, the neck ring arms areopened to release the parison, the invert mechanism returns the neckring arms to the blank side and a blow head support, is displaced from aretracted position to an advanced position, where a supported blow headcloses the blow mold. The parison is blown into a bottle and whensufficiently cooled, the blow head is retracted, the blank molds areopened and a takeout mechanism is displaced to pick up the formed bottleand carry it to a location above a dead plate where it is cooled whilesuspended and then deposited onto the dead plate. In addition to themovement of mechanisms and devices, process air to pneumatic cylindersor to mold cooling systems may also be controlled.

Each section is controlled by a computer which operates under thecontrol of a 360 degree timing drum (programmable sequencer) whichdefines a finite number of angular increments around the drum at whichmechanisms, etc., can be turned on and off each 360 degrees of rotation.Each valve is cycled (turned on and off) and each mechanism is cycledwithin the time of one machine cycle at operator selected “eventangles”.

It is advantageous to operate an I.S. machine at the maximum possiblecycle rate. The degree, to which this has been conventionally achieved,has been a function of the skill of the operator. Highly skilledoperators have been able to run the same bottle, at a faster cycle ratethan is possible with other operators.

To allow any company to operate the machine at a rate, that heretoforeonly the best operators could operate, a control for the IS machine wasdisclosed in U.S. Pat. No. 6,604,383, U.S. Pat. No. 6,604,384, U.S. Pat.No. 6,604,385, U.S. Pat. Nos. 6,604,386, 6,606,886, 6,705,119,6,711,120, and 6,722,158. The teachings of these patents areincorporated herein by reference. In accordance with that control, amachine cycle is defined first by unwrapping the 360 event angle tableinto a constraint diagram. “Unwrapped” means the glass process cyclebeginning with the formation of a gob of molten glass by severing thegob from a runner of molten glass and ending with the opening of thetake out tongs when the formed bottle is located above the deadplate.This process cycle typically takes slightly more than two machine cycleperiods. Then a mathematical representation of the unwrapped cycleconstraint diagram is made that is capable of automated formulation andsolution with the use of quadratic cost equations.

When an I.S. machine is controlled by servo controlled mechanisms, thelimitation of interfering displacements or sequences between the glassand the mechanisms and between the mechanisms can be predicted with afair degree of accuracy. In a conventional I.S. machine, which hasmechanisms displaced with pneumatic motors, this predictability is farless accurate.

OBJECTS OF THE INVENTION

It is accordingly an object of the present invention to provide acontrol system for a glass forming machine of the type above discussedwhich can be easily applied to a conventional I.S. machine.

Other objects and advantages of the present invention will becomeapparent from the following portion of this specification and from theaccompanying drawings, which illustrate a presently preferred embodimentincorporating the principles of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flowchart illustrating the unwrapping of a 360 degreemachine cycle in an I.S. machine into an event time schedule for abottle producing cycle and the optimization of this schedule and itsrewrapping into a 360 degree machine cycle;

FIG. 2 is a portion of an unwrapped cycle constraint diagram for an I.S.machine wherein the two referenced mechanisms are servo operated;

FIG. 2A is an alternate showing of the diagram illustrated in FIG. 2,wherein the two mechanisms are not servo operated;

FIG. 3 is a flow chart of the process of incrementally applying anoptimized schedule using augmented constraints;

FIG. 4 is a geometric interpretation of the process of incrementallyapplying an optimized schedule using augmented constraints;

FIG. 5 is a flow chart of the process of incrementally applying anoptimized schedule using interpolation;

FIG. 6 is a geometric interpretation of incrementally applying anoptimized schedule using interpolation; and

FIG. 7 is a schematic block diagram illustrating the transition of thecontrol for an I.S. machine from its existing cycle to an optimizedcycle.

BRIEF DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 illustrates the use of the computerized model, as disclosed inthe above patents, to define, for an existing machine set up, theoptimized cycle time (Optimized Cycle Time) and the optimized EventAngles for that schedule. With Motion Durations, Sub-motion Durations,Collision Branch Lower Limits, Sequence Branch Lower Limits, EventTimes, Machine Cycle Time, and Optimized Machine Cycle Time/Target/LockStatus known or as inputs to the Optimize Unwrapped Schedule For MinimumCycle Time 82, the Computerized Model 64 will determine whether There IsA Feasible Schedule? 83. If not the model will Reject The Inputs 85. Ifthere is a feasible schedule, the model will Wrap Optimized Event TimesInto Event Angles 84 and Print The Event Angles And The New MachineCycle Time 86 for the schedule cycle so that it will be available forinput into the machine controller portion of the control (“Print”includes updating these event angles in the I.S. machine control). Wherethere is a sub-motion, a portion of the structure's displacement will bein possible interference with some other item and during this sub-motiona collision could result. Sequence branches deal with the reality thatsome events must happen before other events, such as the blank moldsmust close before the baffle can be moved to close the molds. Thermalforming times are times when heat is being removed from the glass orwhen some glass forming process, like blowing or pressing, etc., istaking place. For example, when a parison is blown into a bottle in theblow mold, heat will be transferred from the blown bottle at the moldsurface until the blow mold is opened. When the operator locks thethermal forming times during an optimization process, the glass processwill remain unchanged. “Target” indicates that a value has beenintroduced that the operator is hoping to achieve.

FIG. 2 illustrates a portion of an unwrapped cycle constraint diagramfor an I.S. machine in which servo motors operate the blowhead andtakeout mechanisms. A complete discussion of this drawing is presentedin the cited patents but for purposes of discussion here, “n” connotes anode, “e” connotes that two attached nodes are at the same time, “m”connotes a submotiom, “M” connotes a complete motion, “cz” connotes acollision zone and “c” connotes that the two mechanisms collide. Asillustrated there are three collision zones, each of which can result ina collision between these two mechanisms and the computerized model cantake each into consideration in its analysis.

In accordance with the present invention, the portions of this drawingwhich relate to potentially colliding mechanisms, where one or all ofthe mechanisms does not operate with a servo motor, are redrawn as “usercollision branches”. FIG. 2A illustrates a “user collision branch” whichrepresents the situation where two potentially colliding mechanisms (theblowhead and the takeout) are not both operated with servomotors (hereneither is operated with a servomotor). The fact that a collision canoccur (“takeout in collides with blowhead”) is illustrated in this usercollision branch “c” which is connected between the start nodes (n1,n3)of the two motion branches. The collision branch could also be connectedbetween the end nodes for these mechanisms. The drawing states that if“blowhead up” starts at n1 and concludes at some time n2 thereafter, and“takeout in” starts at n3 (a time latter than n1) and concludes at n4,there will not be a collision. These start times will be known from anexisting event angle chart. FIG. 2A simply provides that if the takeoutstarts n3-n1 after n1, there will be no collision. This modification tothe model will be made whenever a collision can occur between twomechanisms that are not both operated with servo motors. In a usercollision branch, the minimum time between the start of the twomechanisms will be the time defined by reference to the current eventangle chart. The user, can lower this lower limit should some time beavailable as judged by user observation.

Once the optimized schedule is determined, it is applied to theoperating machine without disrupting the glass making process. Toaccomplish this, the event time schedule is modified in small incrementsfrom its current operation to the final optimized schedule in a processthat will be referred to as “incremental application”.

A flowchart providing a high level overview of an optimization sessionis shown in FIG. 3. The session is initiated at 202. Limits areinitialized by 204 such that the collision and sequence margins will notbe any worse than they are with the current job timing. The user thenmodifies, as required, the current target and limit values for thenetwork branches through the user interface 206. Using these settings,an optimization is performed and a preview of the optimal solution isprovided to the user by 208. This preview includes the optimizedduration of the network branches, as well as an indication of the activelimits and how they should be adjusted to allow the optimal solution tobe closer to the target values. The user then observes the operation ofthe machine 210 and assesses whether the suggested adjustments to theactive limits are acceptable. (e.g. is a particular pair of mechanismstruly on the verge of colliding or is there remaining margin?) Basedupon the previewed results, and users observations, the user can electthrough decision block 212 to make further modifications to theoptimization settings by returning to 206, discontinue the session andnot change the event timings 214, or to continue and apply the changes.If the user continues, the timing of the machine will be movedincrementally from its current state to the optimized timing by 216.Each execution of 216 changes the event angles by at most, someprespecified maximum increment. After each such incremental change, theuser observes the operation of the machine 218 to verify that there areno imminent collisions, sequencing problems or undesirable affects tothe ware formation. Based upon this observation, the user can electthrough decision block 220 to make the next incremental change byreturning to 216, make further modifications to the optimizationsettings 206, or discontinue the optimization process. If the userdiscontinues the optimization process, the settings (persistent data)are stored at the user's option by 222 and the session is ended 224.

In general, the event angles on all sections must be modified whenoptimizing the machine speed. This is because all sections must operateat the same speed and the optimal event timing for each section dependsupon the machine speed. The maximum achievable speed of the machine islimited, by the maximum achievable speed of the slowest section. All ofthe sections will be optimized to run at the maximum achievable speed ofthe slowest section.

Two variants of the process of incrementally applying an optimizedschedule are detailed in FIGS. 4 through 7. The use of augmentedconstraints is flow charted in FIG. 4 and a geometric interpretation ofthis approach is provided in FIG. 5. An alternative approach, based uponinterpolation, is flow charted in FIG. 6, and a geometric interpretationof this approach is shown in FIG. 7.

Incremental Application using augmented constraints is one approach tocreate intermediate schedules of events and their associated cycle times(FIG. 4). In the augmented constraint approach, a constrainedoptimization problem is repeatedly solved with an augmented version ofthe original constraint function. Specifically, the constraint functionof the original (preview) optimization is augmented with additionalconstraints that limit the maximum amount that each unwrapped event timecan change from its current value. This process is detailed in theflowchart shown in FIG. 6. The process begins with input 604 of theparameters of the original, non-incremental, constraint function, andcost functions, maximum allowable change in any event angle or maximumallowable change in any event time, maximum allowable change in cycleperiod, current cycle period, current unwrapped event times. If it isnot provided as an input, the maximum allowable change in any event timeis calculated by 606 using: ${\delta\quad t} = \begin{matrix}\frac{\delta\quad\theta}{360} & ( {T - {\delta\quad T}} ) & {speedup} \\\frac{\delta\quad\theta}{360} & T & {slowdown}\end{matrix}$where:

-   δt=magnitude of maximum allowable change in any event time-   δδ=magnitude of maximum allowable change in any event angle-   T=cycle period-   δδ=magnitude of maximum allowable change in cycle period    Since the change in an event time for a given change in event angle    depends upon the cycle period, the above formula selects the more    limiting value. This will be conservative for any intermediate value    of the actual cycle time change.

The base event times are defined to be equal to the current event timesby 608. An upper bound on new event times is set by 610 by adding themaximum allowable event time to the base time. Similarly, the lowerbound is computed by 612 by subtracting the maximum allowable changefrom the base times. In 613 upper bounds on the cyclic branch durationsare computed by adding and the maximum allowable change in cycle periodto the current cycle period and lower bounds are computed by subtractingthe maximum allowable change in cycle period from the current cycleperiod. The existing constraint function is augmented with these upperand lower bounds on admissible event times and cyclic branch durationsby 614. A constrained optimization using the original cost function andaugmented constraint function is performed by 616. The resulting newunwrapped event times are then wrapped around a 360 drum by 617 toproduce a new set of event angles. The new event angles are output by618. The process completes at 620 awaiting another request by the userto further increment toward the final optimized schedule or terminateswhen the non-incremental solution is reached.

This approach can be further understood by considering a geometricinterpretation. In general, a schedule consisting of N event unwrappedevent times can be considered as a single point in an N dimensionalspace. This is illustrated in FIG. 5 for a schedule that has only twoevent times. Any particular schedule is plotted as a point in the twodimensional plane 702 whose horizontal coordinate represents the eventtime for one event in the schedule, and vertical coordinate representsthe second event in the schedule. On this plane we show level lines 704of the cost function and constraint boundaries 706 and 708 for theoriginal problem. The incremental application process begins at somestarting schedule 710, which becomes the base time for the firstapplication. The additional augmented constraints on the maximumallowable change can be visualized as the box 712 surrounding the basepoint 710. This augmented, constrained optimization problem is solvedyielding the next schedule 718, which is at one of the augmentedconstraint boundaries. This becomes the new base point and the processis repeated following a path 714 until the final schedule 716 isreached.

In the interpolation approach, we find new schedules by interpolatingbetween the initial and final (preview) schedules. This process isdetailed in the flowchart shown in FIG. 6. The process begins with input804 of the current unwrapped event times, final optimized unwrappedevent times, maximum allowable change in any event angle or maximumallowable change in any event time, maximum allowable change in cycleperiod and current cycle period. If it is not provided as an input, themaximum allowable change in any event time is calculated by 806 using:${\delta\quad t} = \begin{matrix}\frac{\delta\quad\theta}{360} & ( {T - {\delta\quad T}} ) & {speedup} \\\frac{\delta\quad\theta}{360} & T & {slowdown}\end{matrix}$where:

-   δt=magnitude of maximum allowable change in any event time-   δδ=magnitude of maximum allowable change in any event angle-   T=cycle period-   δδ=magnitude of maximum allowable change in cycle period    Since the change in an event time for a given change in event angle    depends upon the cycle period the above formula selects the more    limiting value. This will be conservative for any intermediate value    of the actual cycle time change.

The base event times are defined to be equal to the current event timesby 808. The change in each individual event time from its current valueto its final optimized value is computed by 810. The event time withgreatest magnitude change is determined by 812. The fraction of theoverall change which can be made without changing this most sensitiveevent time by more than the allowable limit is calculated by 814. Theallowable fraction of the overall change that can be made withoutchanging the cycle period by more than the maximum allowed limit iscalculated by 815. The smaller of the fractions calculated by 814 and815 is selected by 821. A new schedule is then calculated by 816 byincrementing the individual base event times by the product of thefraction computed by 821 and the overall change in the individual eventtime computed by 810. The resulting unwrapped event time schedule iswrapped around a 360 drum by 817 to produce a new event angle schedule.The new event angles are output by 818. The process completes at 820awaiting another request by the user to further increment toward thefinal optimized schedule or terminates when the non-incremental solutionis reached.

This approach can be further understood by considering the geometricinterpretation illustrated in FIG. 7 for a simple two-dimensional(schedule with two event times) case. As discussed previously inreference to FIG. 5, any particular schedule can then plotted as a pointin a two dimensional plane 902. New schedule points 906 are interpolatedalong the line 908 connecting the initial schedule 904 and 912. Schedulepoints are spaced along the line so as not to exceed the maximumallowable per step change in any event time 910. In this example, thiswould be dictated by the change in the horizontal coordinate because agiven movement along the line 908 will produce a greater change in thehorizontal than in the vertical coordinate. (This assumes that thelimiting factor is the maximum allowable change in event angles. If thelimiting factor were the maximum allowable change in speed, the distance910 would be further reduced).

It is noted that the current cycle period is determined by the durationof any cyclic branch in the network model. Thus the cycle time isimplicit in the N dimensional representation of the schedule vector.Also, as an alternative to supplying the incremental optimizationroutine with the current cycle period, it could be obtained from thecurrent unwrapped event times, and the indices associated with the endsof a cyclic branch.

FIG. 8 shows the incremental application procedure. An operator willDefine Optimized Event Time Schedule 920. The operator will thenDetermine A Plurality of Sequential Intermediate Event Time Schedules byIncremental Application 922. The operator will then Unwrap Event TimeSchedules Into Event Angle Schedules 924 and Sequentially Input EventAngle Schedules Into I.S. Machine Control.

1. A control for a glass forming machine which includes a number ofdisplaceable mechanisms and processes which are operated at discretetimes within a machine cycle, wherein an event angle table defines thetimes in a machine cycle when each mechanism or process is operated,wherein the glass forming machine will transform a gob of molten glassinto a bottle in a glass process that takes more than two machine cyclesto complete, and wherein the machine cycle event angles are unwrappedinto glass process event times and presented as a computerized modelcomprising a computer for analyzing the computerized model as aconstrained optimization problem to determine an optimized schedule ofprocess event times, and for determining a plurality of sequentialintermediate schedules of process event times.
 2. A control for a glassforming machine according to claim 1, wherein said intermediateschedules of process event times are determined by linear interpolation.3. A control for a glass forming machine according to claim 1, whereineach of said intermediate schedules of process event times aredetermined by analyzing the computer model as a constrained optimizationproblem.